As semiconductor lasers using nitride III–V compound semiconductors such as AlGaInN, single beam type lasers have been developed and has entered a phase of practical applications as light sources of high-density optical discs, and the like.
On the other hand, for application of a semiconductor laser using nitride III–V compound semiconductors to a light source of a laser beam printer, it is necessary to realize a multi-beam semiconductor laser in which two beams or four beams can be driven independently.
The Applicant proposed a two-beam semiconductor laser using nitride III–V compound semiconductors as shown in FIG. 1 as a multi-beam laser (Extended abstract, Japan Society of Appl. Phys., 62nd Technical Meeting, September 2001, 14p-N-9). As shown in FIG. 1, in this two-beam semiconductor laser, an n-type GaN layer 102 is grown on a c-plane sapphire substrate 101, and GaN compound semiconductor layers forming a laser structure are stacked thereon sequentially, namely, an n-type AlGaN clad layer 103, an n-type GaN optical guide layer 104, an active layer 105, a p-type GaInN intermediate layer 106, a p-type AlGaN cap layer 107, a p-type GaN optical guide layer 108, a p-type AlGaN clad layer 109 and a p-type GaN contact layer 110, to form a mesa portion as a whole. In this case, the uppermost part of the GaN compound semiconductor layers forming the laser structure, namely, the upper part of the p-type AlGaN clad layer 109 and the p-type GaN contact layer 110 are shaped into two ridges 111, 112 extending in parallel. Furthermore, an insulating film 113 covers the mesa portion. The insulating film 113 has openings 113a, 113b above the ridges 111, 112, and p-side electrodes (anode electrodes) 114, 115 are formed in contact with the p-type GaN contact layer 110 through the openings 113a, 113b. Furthermore, a p-side electrode (anode electrode) 116 covers the p-side electrodes 114, 115 and the insulating film 113. The part of the insulating film 113 in contact with the mesa structure has openings 113c, 113d, and n-side electrodes (cathode electrodes) 117, 118 are formed in contact with the n-type GaN layer 102 through the openings 113c, 113d. 
However, the two-beam semiconductor laser shown in FIG. 1 cannot drive individual laser structures independently, and it cannot be directly used as the light source of a laser beam sprinter.
On the other hand, Japanese Laid-Open Publication No. 2000-269601 proposes a multi-beam semiconductor laser although it used semiconductors other than nitride III–V compound semiconductors. However, it is difficult to employ the structure disclosed in this publication cannot directly in semiconductor lasers using nitride III–V compound semiconductors because sapphire substrates exclusively used therein as their substrates are electrically insulating and both the p-side electrodes and n-side electrodes must be lead out from one side of the substrate.
It is therefore an object of the invention to provide a multi-beam semiconductor laser using nitride III–V compound semiconductors, which can drive its individual laser structures independently and can be easily examined in operations before packaging.
It is a more general object of the invention to provide a multi-beam semiconductor laser using nitride III–V compound semiconductors or other semiconductor materials, which can drive its individual laser structures and can be easily examined in operations before packaging.
It is a yet more general object of the invention to provide an integrated semiconductor light-emitting device and a semiconductor device using nitride III–V compound semiconductors or other semiconductor materials, which can drive its individual laser structures and can be easily examined in operations before packaging.